Telephone-exchange system



. Sept 16, 1924.

- A. E. LUNDELL TELEPHONE EXCHANGE SYSTEM Filed July 14. 1917 4 Sheats-$heet 2 Sept. 16. 1924. v 1,508,404

A. E. LUNDELL.

TELEPHONE EXCHANGE .SYSTEM Filed July 14'. 1917 4 sheets-sheet 3 q H i w n I l-1 Sept. 16. 2924;

1,508,404 A. E. LUNDELL TELEPHONE EXCHANGE SYSTEM' Fil ed July 14. 1917 4 Sheets-Shoot 4- fly 4/234 reglsters.

Patented Sept. 16, 1924.

t T E S ALBEN E. LUNDELL, OF NEW YORK, N. Y., ASSIGNOR TO "WESTERN ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed J'ulyl, 1917. Serial No. 180,595.

To all whom it may concern Be it known that I, ALBEN E. LUNDELL, a citizen of the United States,-residing at New York, in the county of Bronx and State of New York, have invented certain new and useful Improvements in Telephone-EX- change Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to an indicating arrangement adapted to be used in a telephone exchange system for the purpose of indicating to an operator the number of a telephone line.

In systems of this kind, especially those in which the indicating device has been operated in response to code impulses transmitted over an impulse transmitting circuit, it has formerly been customary to employ a ground return circuit. Due to the daily variations in the ground potential, ground return circuits cause various operating difficulties.

It is the purpose of this invention to obviate these difliculties by the provision of a metallic signaling circuit. 1

Other features of the invention not specifically referred to above will appear from the following description and claims.

The drawings, with Fig. 2 placed below Fig. 1, with Fig. 3 at the right of Fig. 1 and with Fig. 1 placed below Fig. 3, represent diagrammatically a portion of a telephone system employing the present invention. Only so much of the system is disclosed as is necessary for a clear understanding of the same.

The selector switches used in this system are of the type illustrated in the patent to Craft-Reynolds No. 1,123,696 of January 5,

v 1915, while the circuits for operating these switches are fully disclosed in the patent to Lundell No. 1,168,319 of January '18. 1916.

In thisdescription, reference will be made to sequence switches, registers and impulse The structure of these devices is shown in the patent to Reynolds-Bald win No. 1,127 ,808, and is similar in operation and. function to the sequence switch disclosed in the patent to McBerty No. 1,125,579. The "arrangement of the register, key sets and counting relay arrangement employed in this system are more fully shown in the patent to Lundell No. 1,168,319, above referred to.

It is believed that the operation of this system will best be understood'by tracing the operation of extending the calling sub;

scribers line to a connecting operators po sition, and also describing the transmission of impulses to actuate the number indicating ilevice to indicate the number of the wanted l/Vhen the subscriber, whose substation is indicated at 100, removes his receiver from its switchhook, the line relay 101 is actuated in the well known manner to cause thelighting of the lamp signal 102. An answering operator, on noting the lighting of the signal, inserts an answering plug 103 into the jack 1040f the calling line. This oper ation serves to energize the relays 105 and 106. The energizing circuit of these relays may be traced from grounded battery, winding of cut-off relay 105, sleeve of jacklO f, sleeve of plug 103, winding of relay106, to ground. The cut-off relay 105 is energized and causes the deenergiza tion of the line relay 101, and this relay, upon deen ergization, extinguishes the lamp 102. After the operator inserts the plug 103 into the jack 104, she depresses thefstart key 107. This closes a circuit from grounded battery, magnet of the sequence switch 108, contact 109, start key 107,,to ground. v"Undertlie control of this circuit, the sequence switch 108 moves into position 2. i

In the practical operation of this system, a switch is employed to connect an idle sending device to the cord circuit taken for use.

In the, present disclosure, however, it has.

been not deemed necessary to show this switch, but a sender is shown'individual, to the cord circuit.

Shortly after the depression of start key 107, the operators head set 16 1 is connected to the calling line by means of the listen ing key 165. The operator, upon ascertaining the number of the desired line, which we may assume is 54, party W, depresses the keys 203, 204, 205 and 206 of herky S81},

corresponding to this number. As soon as these keys have been depressed, the register PATENT orric. 1

207 and impulse registers 208,. 209 and- 210 are energized in parallel. The energizing circuit for the district register 207 extends from grounded battery, magnet of the register 207, right-hand armature andback con.- tact of stop relay 211, conductor 212, through the keys 206, 205, 204 and 203, to ground The ene g zi g cireuits f r the impulse registers 208, 209 and 210 may be similarly traced through the right-hand armatures and back contacts of the stop relays 213, 214 and 215, respectively, to ground at the depressed district key 203. The register 207 rotates until it is positioned in accordance with the depression of the proper district key, which takes place when the relay 211 is energized over a circuit traceable from grounded battery, Winding of the stop relay 211, contact 216, and left-hand contact of the depressed district key 203, to ground. The stop relay is energized in this circuit and at its right-hand armature and back contact interrupts the operating circuit of the register 207. Similarly, impulse registers 208, 209 and 210 rotate until they assume positions corresponding to the depressed keys 20-1, 205 and 206- When this takes place, the stop relays 213, 214 and 215 interrupt the operating circuits of their respective impulse registers 208, 209 and 210. As soon as the stop relays 211, 213, 214: and 215 are all energized, a circuit is completed from ground, through the left-hand front contacts and armatures of these relays in series, conductor 217, contact 218, conductor 219, magnet of sequence switch 220, to grounded battery, to move the sequence switch into position 2. 1n position 2 of sequence switch 220 a circuit is extended from grounded battery, windings of the magnets 270 to 273 in parallel, contact 275, to ground, to release the keys 203 to 206. The regis ters 207 to 210 remain in their set positions until they are again operated by the depression of the keys in accordance with new number. lVhen the sequence switches 108 and 220 reach position 2, the line relay 110 is energized over a fundamental circuit extending from grounded battery, winding of relay 110, contact 111, conductor 112, contact 200, outer back contact and armature of upper zero counting relay, winding of the stepping relay 201, contact 202, conductor 113, contact 114-, to ground. The line relay 110 is energized in this circuit and attracts its armatures, and, at its right-hand armature, completes a circuit from ground, righthand armature and front contact of relay 110, contact 116, conductor 130, magnet of sequence switch 108, to grounded battery, to move the sequence switch into position 3, At the left-hand armature and front contact of line relay 110, a locking circuit is established for this relay, which may be traced from grounded battery, winding and lefthand front contact and armature of relay 110, contact 117, and to ground over the re mainder of the fundamental circuit previously described.

In position 3 of the sequence switch 108, a circuit is completed for the updrive magnet 118 of the district selector switch, generally designated 119. Under the control of the updrive magnet, the' selector switch is directively set in operative relation to a group of trunks extending to a desired oiiice, and, under the control of this magnet, the selector switch 119 may be further operated to hunt for an idle trunk in the selected group. The energizing circuit of the updrivc magnet 118 is traceable from grounded battery, Winding of this magnet. contact 120, right-hand front contact and armature of line relay 110, to ground. Under the control of the updrive magnet 118, the selector switch 119 elevates its brushes 121, 122, 123, and its commutator brushes 12 1 and 125. Each time that the commutator brush 125 encounters a conducting scgment of the commutator 126, a circuit in shunt of the fundamental circuit, above described, is completed from ground, commutator brush 125, conducting segment of commutator 126, conductor 127, contacts 128 and 117, left-hand armature, front contact and winding of line relay 110, to grounded battery. Each time that the shunt circuit is completed, the stepping relay 201 deenergizes in the well known manner. For each energization of the stepping relay 201, one of the series of counting relays, indicated generally by the numeral 221, is energized. As is well known, the first one of the series of counting relays to be energized is determined by the set position of the register. lVhen the stepping relay 201 has been shortcircuited anumber of times, suiiicient to cause the energization of the remaining counting relays, including the upper zero counting relay 222, a circuit is completed from grounded battery, magnet of sequence switch 220, conductor 21.9, contact 223, inner armature and front contact of the upper zero counting relay 222, to ground. The sequence switch 220 rotates out of position 2 into position 3, and, by so doing, interrupts the fundamental circuit at contacts 200 and 202.

As soon as the fundamental circuit is interrupted, the line relay 110 deenergizes, and, at its right-hand back contact and ar mature, closes a circuit from ground,through contact 129, conductor 1.30, magnet of sequence switch 108, to grounded battery. This circuit operates to move the sequence switch 108 out of position 3 and into position 6.

In position 6 of the sequence switch 108, test relay 132 is energized over a circuit 6X tending from grounded battery, the righthand winding of this relay, contacts 133, 13st, to ground. The test relay 132 attracts its armatures, and, if the first trunk of the selected group is busy, this condition will be indicated by ground potential on its test terminal 131, in which case a locking circuit for test relay 132 is completed from.

inner left-hand front contact and armature of relay 132, conductor 135, test brush 123, test terminal 131, to ground. At the righthand armature and front contact-of the test relay 132, a circuit is completed from ground, contact 136, conductor 130, magnet of sequence switch 108, to grounded battery, to move this sequence switch into position. 7.

In position 7, the updrive magnet 118 is again energized to control the hunting operation of the district selector switch 119. This circuit extends from grounded battery, winding of magnet 118, contact 137, righthand front contact and armature of test relay 132, to ground. As the brushes of the selector switch 119 are elevated over the selected group of trunks, the commutator brush 124, except when the brushes of the selector are properly centered over the trunk terminals, engages the conducting segments of commutator 139 to maintain relay 132 energized. This energizing circuit is completed from grounded battery, right-hand winding of relay 132, contacts 133 and 154, outer left-hand front contact and armature of relay 132, conductor 155, through the conducting segments of the accurate centering commutator 139, brush 124 to ground. When, however, the brushes of the selector switch are properly centered on the terminals of an idle trunk, the test relay 132 deener'gizes, and thereby completesv a circuit for moving the sequence switch 108 out of position 7 and into position 11. This circuit extends from grounded battery, winding of the sequence switch'108, conductor 130, contact 140, right-hand back contact and armature of test relay 132 to ground.

In posit-ion 11 of the sequence switch 108, an impulse transmitting circuit is completed from the A operators position to the B operators position. As soon as the signaling circuit is extended to the B operators'position, a circuit is completed from battery 300, which, in this instance, is shown as being of high voltage, the back contact and lefthand armature of relay 301, left-hand winding of the relay 302, cont-act and spring303, left-hand winding of the repeating coil 304, upper back contact and armature of the relay 305, trunk conductor 306, terminal 141, brush 121, contact 142, conductor 1.12, contact 224, left-hand winding of the relay 225, which winding is of high resistance, the right-hand winding of the relay 225, conductor 113, contact 143, brush 122, terminal 144, trunk conductor 307 lower armature and back contact of the relay 305, left-hand winding of the repeating coil 308, spring 309 and its contact, right-hand winding of relay 302 to ground. The left-hand winding of relay 225 is of such high resistance that it energizes only when it is in-series with the high voltage 300, from which fact it will be seen that the sequence switch 220. which controls the transmission of impulses, is

not moved out. of osition 3 until the controlling relays of t e number indicator are in condition. to receive the code impulses. vVhen the relay-302 attracts its armature, it closes a circuit from ground, I right-hand armature and front contact of the relay 302, conductor 310, lower back contact and armature of relay 311, lamp; signal 312 to grounded battery. The operator notes the lighting of the lamp 312 and depresses the key 313. This operation serves to complete a circuit from ground, winding of the relay 305,, key 313, and off-normal contact 314, winding of the relay 315' to grounded battery... The

relays 305 and 315 attract their armatures,

and, at the right-hand front contact and armature of relay 315, a locking circuit is established for this relay and the relay 305 as long askey 313 is depressed. The relay 305, on energization, connects ground to its.

lower armature, and extends trunk conductor 306 to relay 321,- which controls the operation of the number-indicating device.

As soon as the relay 315 attracts its lefthand armature, a circuit is completed from ground, left-hand armature and front contact of relay 315, switch arm 316, magnet of step switch 317 to grounded battery- The switch thereupon moves its brushes 316, 318,

319 and 320 into their second position. This key 313, the sequence switch 220 was moved out of position 3 into position 4 over a circuit extending from grounded battery, magnet of the sequence switch 220, contact 226, left-hand front contact and armature of the relay 225 to ground. In position 4 of the sequence switch 220, there is substituted, for the original energizing circuit of the relay 225, a holding circuit, which is maintained until the relays of the call-indicating device are in condition to receivethe impulses, or, in other words, until the operator depresses the key 313. This holding circuit has been traced through conductor 112, right-hand' armature and contact of relay 225, contacts 227 and 228, right-hand winding of the relay 225, conductor 113, over the remainder of the circuit previously described. As soon, however, as the operator depresses the key 313, the relay 225 'deenergizes, and, at its left-hand armature-and back contact, completes a circuit from ground, through contact229, magnetof the sequence switch 220 to grounded, battery, to. move the, sequence switch into position. 5. i

It will be noted inthi description that til one of two paths is provided for moving the sequence switch 220 out of its succeeding positions; one path being closed through the contacts of the impulsers and the contacts of sequence switch 220'; the other circuit for the sequence switch being completed through the contacts of sequence switch 220, and through the contact and armature of one of the relays 230, 231, 232 or 233. \Vhen the sequence switch 220 has its operating circuit completed through one of its contacts and one of the contacts of the impulsers, it immediately rotates into its next position and closes or opens the contact 234 of the impulse transmitting circuit for such a short interval that the slow-operating controlling relays do not have an opportunity to attract their armatures. lVhen, however, the operating circuit of the sequence switch 220 is completed through the armature of one of the slow-to-respond relays 230 to 233 which in turn is energized through one of the contacts of the sequence switch 220 and one of the contacts of the impulsers, the sequence switch 220 remains in its various stopped positions for a relatively long interval and closes or opens its contact 234 for an interval of time of suflicient duration to insure the operation of the various controlling relays. From this it will be understood that the long and short impulses transmitted over the impulse transmitting circuit are controlled at the contact 234 of sequence switch 220 and the duration of the closure of this contact is dependent on whether the operating circuit of the sequence I switch 220 is controlled directly through one of its contacts and the contacts of the impulsers or through its contacts and the armature of one of the slow-to-respond relays 230 to 233 that must first operate through one of the contacts of the sequence switch 220 and the contacts of the impulsers.

It will be remembered that the operator depressed the stations key W to set the impulse register 210. With the sequence switch in position 5, a circuit is closed from grounded battery, winding of relay 233, conductor 250, contacts 290 and 236 to ground. The relay 233 attracts its armature and completes a circuit from ground, through contact 237, magnet of sequence switch 220, to grounded battery, to move the sequence switch 220 out of position 5. The contact 234 in position 5 is closed for a long interval. Immediately upon the c1osure of the contact 234, the energizing circuit of relay 321 is closed from grounded battery, Winding of this relay, switch arm 318 in its second position, upper front contact and armature of relay 305, conductor 306, terminal 141, brush 121, contact 142, conductor 112, contact 234, conductor 113, contact 143, brush 122, terminal 144, trunk conductor 307 lower armature and front contact of relay 305, to ground. The circuit just described will hereinafter be referred to as an impulse transmitting circuit. Relay 321 attracts its armatures, and, at its lefthand armature and front contact, closes a circuit from ground, through switch arm 316 in its second position, winding of the motor magnet 317, to grounded battery, to cause the operation of this magnet and the resulting movement of the switch arms into their third position. The movement of the switch arms is rapid, and, since a long im pulse is being transmitted, the controlling relay a: is energized over a circuit extending from grounded battery, its right-hand wiuding, switch arm 319 in its third position, right-hand front contact and armature of relay 321, to ground. Relay (4 attracts its armatures and simultaneously establishes a locking circuit for itself traceable from grounded battery, both windings of the relay a; in series, inner left-hand front contact and armature of relay a, conductor 323, lefthand front contact and armature of relay 315, to ground. The apparatus is now in condition to receive the second stations impulse. It will be remembered that the se quence switch 220 is in position 6. In this position, an energizing circuit for relay 232 is established from grounded battery, winding of this relay, contacts 238 and 239, to ground. The relay 232 attracts its armature, and thereby closes an operating circuit from ground, through contact 240, magnet of the sequence switch 220 to grounded; battery, to move this sequence switch into position 7. It will be seen that the contact 234 in position 6 is opened for a long period, as the result of which the relay 321 retracts its armature long enough to cause the relay 1) to operate over a circuit traceable from grounded battery, right-hand winding of this relay, switch arm 320 in its third posi tion, right-hand back contact and armature of relay 321 to ground. The relay 6. on at tracting its armatures, establishes a locking circuit for itself from grounded battery, through both windings of relay 6 in series, inner left-hand front cont-act and armature of this relay, conductor 323, to ground at the left-hand armature of relay .315. In position 7 of sequence switch 220 an operat ing circuit is completed for this sequence switch from grounded battery, its operating magnet, contacts 241 and 242, to ground. to move the sequence switch into position 8. The contact 234 in position 7 is closed for an interval long enough to cause the relay 321 to attract its armature, and, by so doing, causes the motor magnet 317 to move the switch arms into position 4, but this interval is not long enough to cause the energization of the stations indicator controlling relay 0.

It will be remembered that the op rator of the tens impulse register 208 and close the contacts 243, 244, 245 and 246. When the sequence switch 220 reached position 8,

a circuit was closed from ground, through contacts 247 and 243, conductor 248, magnet of sequence switch 220, to grounded battery, to move the sequence switch into position 9. The contact 234 is thus open for a very short interval and' relay A is not operated. In position 9 a circuit is closed from ground, contacts 249, 246, conductor 250, winding of a relay 233, to groundedv battery. The relay 233 attracts its armature which completes a circuit from ground, contact 237, magnet of sequence switch 220 to grounded battery, to move the sequence switch out of position 9 and into position 10. While the sequence switch was in position 9, the impulse transmitting circuit was closed for a relatively long period and relay 321 attracted its armatures. This caused the motor magnet to move its switch arms into their fifth position and also closed an energizing circuit for the slow-operating relay B, which circuit is traceable from grounded battery, right-hand winding of relay B, conductor 400, switch arm 319 in its fourth position, right-hand front contact and armature of relay 321 to ground. The relay B on attracting its armatures establishes a locking circuit for itself from grounded battery, through both windings in series of the relay B, left-hand contact'and armature of this relay, conductor 401, 402, left-hand front contact and armature of relay 315, tov

ground. In position 10 of sequence switch 220, a circuit is completed from ground, contacts 251, 245, conductor 248, magnet of sequence switch 220, to grounded battery, to move the sequence switch into position 11. It will be seen that the sequence switch 220 does not remain in position 10 long enough to permit the relay 321 to remain inert for a period long enough to cause the energization of the relay G. In position 11 of the sequence switch 220, a circuit is closed from' ground, contacts 252, 244, conductor 248, magnet of sequence switch 220, to grounded battery, to move this sequence switch into position 12. Although the signaling circuit is closed in position 11 of the sequence switch 220, this circuit is closed for a period long enough to cause the energization of the motor-magnet 317 and the resultant movequence switch immediately into position 13,

and relay 321 is not deenergized for a sufi cient interval to cause the energization of relay B In position 13 of the sequence switch 220 the signaling circuit is closed,

but only for a periodlongenough to cause the motor-magnet 317 to move the switch arms into position 7. A circuit is immediately completed for moving the sequence ductor 248, magnet of sequence switch 220,

to grounded battery. In position 14 of sequence switch 220, a circuit is closed from ground, contacts 258, 25 9, conductor 248, magnet of sequence switch 220, to grounded battery, to move the sequence switch into position 15. In position 14 of the sequence switch 220, the signalingcircuit is opened for only a short time, so that the circuit controlled through the right-hand back contact and armature of relay 321 does not opcrate controlling relay B.

. In position 15 of the sequence switch 220, a circuit is completed from grounded battery,winding of relay 231, contacts 261,260, to ground. The relay 231 attracts its armature and closes a circuit from ground through contact 262, magnet of sequence switch-220, to grounded battery, to move this sequence switch out of position '15 and into its normal position. The signaling circuit is completed at contact 234 .and remains closed for a long period. This causes the energization of the relay 32l,,which causes this relay to attract itsarmatures. At the left-hand armature and front contact of this relay, a circuit is closed to energize the motor magnet 317, which magnet moves the switch arms into postition 8. At the right-hand ar-' mature and front contact of relay 321, a circuit is closed from ground, through the switch arm 319 in its eighth position, conductor 403, right-hand winding of relay C, to grounded battery. The relay G" attracts its armatures and at its left-hand armature and front contact completes a locking circuit for itself from grounded battery, through both of its windings in series, its left-hand armature and contact, conductor 402, to ground. While the sequence switch 220 is rotating through position 16 the signaling circuitis momen-- tarily closed to cause the energization of the relay 321, whichin turn causes the motor magnet 317 to operate to move the switch arms into their ninth position. In. this positionthe relay 322 is energized over a 'circuit extending from grounded battery, winding of this'relay, switch arm 320- in its ninth position, right-hand backcont'act and armatureof relay 321, to'ground. There lay 322 controls the lighting of certainnumber indicating lamps. ,In parallelwith relay 322, the relay 40.4 is-energized over a circuit traceable from grounded battery, winding of this relay, conductor 405, switch arm 320 in its ninth position, right-hand back contact and armature of relay 321 to ground.

lVith the various controlling relays actuated, the No. 5 tens lamp is energized over a circuit traceable from grounded battery,

left-hand armature and contact of relay 404,

conductor 406, armature 408 and back con tact of relay A conductor 407, outer righthand armature and front contact of relay B, inner right-hand armature and back contact of relay A, conductor 409, tens lamp No. 5, conductor 410, inner right-hand frontcontact and armature of relay B, outer back contact and armature of relay A, inner right-hand back contact and armature of relay C, conductor 411, inner right-hand front contact and armature of relay 322, conductor 353, left-hand front contact and armature of relay 315, to ground.

No. 4 units lamp is lighted over a circuit extending from grounded battery, righthand armature and front contact of relay 404, conductor 412, inner left-hand armature and back contact of relay B conductor 413, outer right-hand armature and back contact of relay B right-hand middle armature and back contact of relay A conductor 414, outer right-hand armature ant front contact of relay C lamp No. 4, conductor 416, inner right-hand front contact and armature of relay C conductor 417, outer righthand front contact of relay 322, to ground over conductor 323. The stations lamp on is lighted over a circuit completed from grounded battery, right armature and back contact of relay 0, right-hand armature and front contact of relay a, outer left-hand armature and front contact of relay 7), lefthand front contact and armature of relay 322, conductor 323 to ground. The operator on noting the number and party of the desired line inserts the plug 324 into the jack of the desired line and ringing current of the proper frequency to signal the desired substation is applied. It will be understood that any well-known means, either manual or automatic, for selecting the proper ringing current may be employed, but it has been found preferable to employ the automatic means for selecting ringing current, as disclosed in the copending application of A. E. Lundell and E. H. Clark, Serial No. 158,589, filed March 30, 1917.

While the sequence switch 220 was rotating through positions 14 to 18, a circuit was closed from ground, contact 265, conductor 146, contact 147, magnet of sequence switch 108 to grounded battery, to move the sequence switch into position 12 or the talking position. As soon as the operator has ascertained the number of the desired line, she releases the key 313, whereupon relay 315 retracts its armatures and removes ground from the conductors 323 and 402, causing the actuated controlling relays to be restored. Also when relay 315 retracts its armature, a stepping circuit is closed from grounded battery, winding of magnet 317, its back contact and armature, contact 327, left-hand back contact and armature of re lay 315 to ground. The magnet 317, by interrupting its operating circuit, continues to rotate the switch arms to their normal or starting position. At this position the offnormal contact 327 is opened so as to break the operating circuit for magnet 317 and stop the switch. As soon as the plug 324 is inserted into the jack 325 of the desired line, the cutoff relay 326 and relays 311 and 301 are energized over a circuit traceable from ground, winding of relay 326, sleeve of jack 325, sleeve of plug 324, windings of relays 311 and 301, to low voltage battery 330. The relays 301, 311 and 326 are energized in this circuit and the cutoff relay 326 operates in the well-known manner to disconnect the line relay 331 from the called line. The relay 311 at its upper armature and contact closes a break point in the link circuit in which the plug 324 terminates. At the lower armature of the relay 311, the operating circuit of the lamp 312 is interrupted to extinguish this lamp. The relay 301 attracts its armatures and completes an energizing circuit for the relay 302. This energizing circuit is established from grounded battery 330, front contact and armature of relay 301, left-hand winding of relay 302, contact spring 303, left-hand winding of repeating coil 304, upper back contact and armature of relay 305, trunk conductor 306, terminal 141, brush 121, contact 157, righthand winding of repeating coil 158, polarized relay 159, right-hand winding of repeating coil 160, contact 161, brush 122, terminal 144, trunk conductor 307 left-hand winding of repeating coil 308, contact spring 309, and its contact, righthand winding of relay 302, to ground. The relay 302 attracts its armature and as soon as the called subscriber responds, the supervisory relay 333 is energized to complete an energizing circuit for the relay 334. The energizing circuit for this relay extends from grounded battery, Winding of relay 334, contact and armature of relay 333, front contact and armature of relay 302, to ground. The relay 334 in attracting its armatures reverses the direction of the current through the trunk conductors 306, 307, which results in the operation of the polarized relay 159 and the lighting of supervisory lamp 162.

At the conclusion of the conversation, the operators may be informed of this by the well-known supervisory signals. When the A operator removes the plug 103 from jack 104, the relay 106 deenergizes to complete a circuit from ground, armature and back contact of relay 106, contact 1&8, magnet of sequence switch 108, to grounded battery, to move the sequence switch into position 18. In position 18, the down-drive magnet 149 is energized over a circuit traceable from grounded battery, Winding of magnet 14:9, contact 150, to ground. Under the control of the down-drive magnet the district selector switch 119 is restored to its normal position. In this position the commutator brush 125 encounters a conducting segment of commutator 126 and completes a circuit from ground, conductor 151, contact 152, conductor 130, magnet of sequence switch 108, to grounded battery. Under the control of this circuit the sequence switch rotates into its normal position.

What is claimed is:

1. In a telephone system, an originating oflice, a terminating ofiice, a trunk line eX- tending between said oiiices, an impulse transmitting device, switching means controlled by said impulse transmitting device for connecting the device to said line, a variably operable indicating device operable in response to impulses over two sides of said line in series, means for disabling said impulse transmitting device until said indicating device is in condition to operate, and manually operable means for conditioning said indicating device to respond to said impulse transmitting device.

:2. In a telephone system, an originating office, a terminating office, a trunk line extending between said offices, an impulse transmitting device, switching means controlled by said impulse transmitting device for connecting said device to said line, a variably operable indicating device controllable in response to impulses over two sides of said line in series, means for disabling said impulse transmitting device, and manually operable means at a distant point for controlling said disabling means to permit impulses to be transmitted.

3. In a telephone system, an originating office, a terminating oifice, a trunk line extending between said offices, a code impulse transmitting device, switching means controlled by said impulse transmitting device for connecting said device to said line, a variably operable indicating device normally disconnected from said line, controllable in response to impulses over two sides of said line in series, and means for connecting said indicating device to said line.

4:. In a telephone system, a telephone line, a signaling circuit serially including a portion of two sides of said line, a number ina signaling circuit serially including a portion of two sides of said line, an interrupting contact included in said circuit, a number indicating device responsive to interruptions in said signaling circuit, directively operable means for operating .said contact to cause interruptions of various durations in said signaling circuit, and means for disabling said last mentioned means until said number indicating device is in condition to be operated.

6. In a telephone system, a telephone line, a signaling circuit serially including a portion of two sides of said line, an interrupting contact included in said circuit, a number indicating device responsive to interruptions in said signaling circuit, directively operable means for operating said contact to cause interruptions of Various durations in said signaling circuit, and means controlled from said number indicating device for disabling said last mentioned means until said number indicating device is in condition to be operated.

, 7. In a telephone system, a semi-mechani- I cal ofice, a manual office, trunk lines connecting the same, an impulse transmitting device at said semi-mechanical oiiice, a selector switch for connecting said device to any of said trunk lines, an indicating device at said manual office arranged to be controlled over two sides in series of any of said trunks,

and a manually operable means for starting said impulse transmitting and indicating devices. 1

8. In a telephone system, a semi-mechanical oiiice, a manual office, trunk lines connecting the same, a variably operable impulse transmitting device at said semimechanical oflice arranged to be connected to any of said trunk lines, a number indicating device at said manual office arranged to be operated in response to impulses over two sides in series of any of said trunks, means at said manual office for disabling said impulse transmitting device until said number indicating device is in condition to be operated, and means for disconnecting said disabling means from said impulse transmitting device.

In witness whereof, I hereunto subscribe my name this 11th day of July A. D., 1917.

ALBEN E. LUNDELL. 

